Method for stabilizing x-ray emulsions to red safelights



United States Patent 3,411,914 METHOD FOR STABILIZING X-RAY EMULSIONS TORED SAFELIGHTS Claude Dostes, Joinville-le-Pont, France, assignor toEastman Kodak Company, Rochester, N.Y., a corporation of New Jersey NoDrawing. Filed July 13, 1964, Ser. No. 382,407 Claims priority,application France, Dec. 5, 1963, 956,168 6 Claims. (Cl. 96-101)ABSTRACT OF THE DISCLOSURE Photographic silver halide emulsions areprepared by adding, after the end of the after-ripening step, first atetrazaindene salt and then a noble metal salt. These emulsions havegood sensitivity to image-forming radiation shuch as X-ray intensifierscreen emissions and are substantially insensitive to red safelights.

This invention relates to photographic emulsions, and more particularlyto photographic emulsions containing tetrazaindene antifoggants, whichemulsions are not fogged by red safelights.

It is known to incorporate various tetrazaindene compounds, such astetrazaindene salts, in photographic emulsions as antifoggants. Whilethese compounds provide lgood fog control, they absorb some redradiation causing fog in the emulsion when handled in the pres ence ofconventional red safelights. It therefore appears desirable to provideemulsions containing tetrazaindene salt antifoggants, which emulsionsare not fogged by red radiation such as that emitted from redsafelights.

One object of my invention is to provide photographic emulsionscontaining terazaindene salts, which emulsions are substantiallyinsensitive to commonly employed red safelights. Another object of myinvention is to provide a method of preparing photographic emulsionscontaining tetrazaindene salts, which emulsions are substantiallyinsensitive to red radiation such as that emitted by commonly employedphotographic red safelights. Other objects of my invention will appearherein.

These and other objects of my invention are accomplished by providingphotographic emulsions which contain a noble metal salt and atetrazaindene salt which is an antifoggant for photographic silverhalide emulsions.

The preparation of silver halide emulsions involves three separateoperations: (1) the emulsification and digestion or ripening of thesilver halide; (2) the freeing of the emulsion from aqueous solublesalts usually by washing; and (3) the second digestion or after-ripeningto obtain increased sensitivity (Mees, The Theory of the PhotographicProcess, 1954, p. 4). In accordance with my invention, the noble metalsalt and tetrazaindene salt are incorporated in the emulsion subsequentto the afterripening step or second digestion. In order to obtainsatisfactory results, it is necessary to first add the tetrazaindenesalt to the emulsion, and then the noble metal salt, followed by a shortperiod of digestion.

The addition of only a gold salt (or noble metal) salt to an emulsion atthe end of the after-ripening step, or thereafter, lowers thesensitivity of the emulsion to red radiation, but causes an undesirabledesensitization of the emulsion to image-forming radiation. However, theaddition of tetrazaindene salt and noble metal salt in that ordersubsequent to after-ripening of an emulsion provides an emulsion havinggood sensitivity to image-forming radiation and which is substantiallyinsensitive to red radiation.

My invention will be further illustrated by the following example.

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EXAMPLE I A coarse grain silver bromoiodide emulsion of the type used inmedical X-ray films was prepared in the customary manner, sulfursensitized in accordance with Sheppard U.S. Patent 2,410,689, and afterthe second digestion, while the emulsion was cooling at a temperature ofabout 50 C., 1 gram 4-hydroxy-6-methyl-1,3,3a,7- tetrazaindene sodiumsalt per mole silver was incorporated in the emulsion, and immediatelythereafter 1.3 mg. potassium chloroaurate per mole of silver was addedto the emulsion. The temperature of the emulsion was held at about 50 C.for about 10 minutes, and then allowed to cool. The emulsion was coatedon a support and subjected to radiation from a commonly used redsafelight. The emulsion was found to be essentially free from fogwhereas a control emulsion, which was the same as the test emulsionexcept that the noble metal salt was added before the tetrazaindenesalt, was badly fogged when tested in the same manner. The emulsion inaccordance with the invention possessed good sensitivity to X-rayintensifying screen radiation. The addition of the salts in accordancewith the invention does not modify the sensitivity of the emulsion toX-ray radiation.

In accordance with the invention, I may use any of the tetrazaindenesalts which are antifoggants for silver halide emulsions and whichimpart red sensitivity to the emulsion, for example, those described byCarroll et al. U.S. Patent 2,716,062 or Tinker et al. U.S. Patent2,835,- 581, in the form of their alkali metal or ammonium salts.Particularly suitable are the 4-oxo or 4-hydroxytetrazaindenes, e.g.,salts of the 4-hydroxy-l,3,3a,7- tetrazaindenes. These tetrazaindenesmay contain various substituents, such as hydroxy, alkyl, amino andcarboxyl. The salts may be conveniently prepared, for example, byreacting hydroxyl or carboxyl containing tetrazaindenes with an alkalimetal hydroxide. The tetrazaindene salt may be employed in amounts offrom 0.25 to 10, and preferably 1.0 to 5.0 g. per mole of silver.

Preferably, the noble metal salts which are employed are water soluble,although insoluble noble metal salts may be used. Representative saltsof the noble rnetals, such as ruthenium, rhodium, palladium, iridium andplatinum, which may be used include ammonium chloropalladate, potassiumchloroplatinate and sodium chloropalladite. Advantageously, a solublegold salt is used, potassium chloroaurate being particularly suitable.Other representative useful gold salts include potassiumaurithiocyanate, auric trichloride and 2-aurosulfobenzothiazolemethochloride. The noble metal salts are preferably employed in amountsof 1.0 to 5.0 mg. per mole of silver, although the most useful range is0.25 to 10 mg. per mole of silver.

The independent addition to an emulsion of a noble metal salt subsequentto after-ripening of the emulsion lowers the sensitivity to redradiation. If desired, a noble metal salt may also be added to theemulsion before the after-ripening to increase sensitivity;advantageously, a gold salt is employed. In this instance, othersensitizers may be used with the gold (or noble metal) salts if desired,such as sulfur sensitizers, for example, those described in Sheppard etal. U.S. Patents 1,574,944, 1,623,- 499 and 2,410,689.

As indicated above, the tetrazaindene salt is added to the emulsionfirst and then the noble metal salt is incorporated therein. The saltsmust be added to the emulsion at the earliest, at the end of theafter-ripening or second digestion, or anytime thereafter. It isnecessary to add the tetrazaindene salt subsequent to the after-ripeningstep in the emulsion preparation since such salts would inhibit theeffect of chemical sensitizers it added at an earlier stage of theemulsion preparation.

The addition of the tetrazaindene and noble metal salts is followed by ashort period of digestion of the emulsion, such as from about 1-10minutes at about 50 C. Advantageously, the salts are added duringcooling of the emulsion after the second digestion, and while theemulsion is at about 50 C.

The invention is applicable to emulsions containing tetrazaindene saltantifoggants, which emulsions are not spectrally sensitized, or arespectrally sensitized only to the green region of the spectrum. Theinvention is particularly useful with medical X-ray emulsions which arenot spectrally sensitized, but which may, of course, be chemicallysensitized.

Emulsions in accordance with the invention have good fog stability andare substantially insensitive to the conventional red safelightsemployed in the photographic industry. Such safelights may be prepared,for example, by covering a 15 or 25 watt tungsten bulb with a filterwhich transmits light substantially only in the red region of thespectrum.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

I claim:

1. In a method of preparing photographic silver halide X-ray emulsionscontaining tetrazaindene salt antifoggant, which method comprises thesteps of emulsification, removal of soluble salts and after-ripening,and separate additions' following the after-ripening step of both atetrazaindene salt and from 0.25 to mg. per mole silver of a noble metalsalt to said emulsion, the improvement wherein said additions followingthe after-ripening step are performed in the order of first adding saidtetrazaindene salt and thereafter adding said noble metal salt wherebyred-safelight sensitivity of the emulsion is maintained below thered-safelight sensitivity that would obtain by opposite order of saidadditions.

2. An improved method defined by claim 1 further comprising a step ofdigesting the emulsion for a short time following the defined additionsof tetrazaindene and noble metal salts.

3. A method defined by claim 1 wherein the defined tetrazaindene salt isa Water-soluble 4-oxotetrazaindene salt and the defined noble metal saltis a water-soluble gold salt.

4. A method defined by claim 1 wherein the defined tetrazaindene salt isan alkali metal salt of a 4-hydroXy-1,3, 3a,7-tetrazaindene and thedefined noble metal salt is a water-soluble gold salt.

5. In a method of preparing photographic silver halide X-ray emulsionscontaining tetrazaindene salt antifoggant, which method comprises thesteps of emulsification, removal of soluble salts and after-ripening,the improvement which comprises first adding to the emulsion, while itis cooling subsequent to the after-ripening step, at about C., about 1g. per mole silver of 4-hydroxy-6-methyl- 1,3,3a,7-tetrazaindene sodiumsalt, and following said first addition adding to the emulsion about 1.3mg. per mole silver of potassium chloroaurate.

6. A photographic emulsion prepared in accordance with the method ofclaim 1.

References Cited UNITED STATES PATENTS 2,597,856 5/ 1967 Damschroder96-108 X 2,716,062 8/1955 Carroll 96-109 X NORMAN G. TORCHIN, PrimaryExaminer. R. E. FICHTER, Assistant Examiner.

